This invention relates to apparatus and a method of monitoring movement of objects in a monitoring region.
In U.S. Pat. No. 5,519,784 there is disclosed apparatus and a method of classifying movement of objects along a passage. The apparatus comprises means for projecting an array of discrete and spaced parallel linear radiation beams from one side of the passage to an opposite side of the passage. Detectors at the opposite side of the passage sense when the beams are interrupted by one or more persons moving in the passage in either of a first and a second opposite direction. The spaced beams are interrupted at different times in a sequence corresponding to the number of and direction of movement of persons. The sequentially generated interrupted beam signals are stored as object movement historic information in memory and then processed to generate composite beam interrupt patterns manifesting the number of persons and direction of movement, the patterns being a function of time domain and sensor index, i.e. sensor identity and position in the passage. The resulting generated patterns are compared to reference patterns utilizing computerized pattern recognition analysis, such as with an artificial neural network. The comparison classifies the persons in the passage into direction of movement and number.
This apparatus and method may not be suitable for some applications. For example, the means for projecting the spaced parallel beams is mounted in an elongate housing. The housing is normally mounted on one side of the passage to extend parallel to the floor at about between ankle and knee height. This housing may be too large to fit into available space therefor and/or may not be aesthetically acceptable in certain applications. Furthermore, it is labour, time and cost intensive to mount this apparatus on either side of the passage and it often is necessary to chase into the side-walls of the passage to install cabling extending to the apparatus. Still furthermore, the beam projecting means on the one side and the detectors on the other side may become misaligned, which would cause the apparatus to cease functioning. Another problem with this side-on mounted apparatus is that a person or object stationary in the passage could interrupt the beams and hence cause at least temporary insensitivity of the apparatus to other objects moving along the passage on either side of the stationary object. Still a further problem is that the range of the projected beams may not be sufficient to traverse a wide passage. Intermediate structures carrying additional apparatus with all of the aforementioned disadvantages are required to cover the wide passage.
Another known system, but which is fundamentally different, uses tracking algorithms and attempts to identify discrete objects and monitor their position between successive frames produced by an object sensing arrangement, in order to determine a vector for each object of interest. The processing is complex, as it requires a full analysis of each frame and then a comparison to previous frames to determine whether an object is either a previous object in a new position or a new object altogether. Tied in with this, is the difficulty in distinguishing between two people on the one hand and one person carrying a backpack or luggage, for example, on the other. By isolating objects and obtaining their vectors, the system is able to track their movement across a predetermined monitoring region and thus increment or decrement counts accordingly. Any inability of the system to isolate objects, link their successive positions or distinguish number of objects compromises the accuracy of the system. In addition, the visual analysis is extremely processor-intensive and thus expensive.